Mutual Damage

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  Difficulty: Intermediate   Keywords: EndGame

Table of contents Table of diagrams
Question starts here
No mutual damage
Mutual damage
B defends - loss by 1 point
Mutual damage
Mutual damage - W is no hope

Introduction

The general principle of mutual damage is to accept loss of territory, rather than defend territory, provided one can inflict equivalent damage on the opponent. Hence, mutual damage is a like a kind of exchange.

Defending is a way to accept gote. If you pursue a mutual damage plan, not answering the opponent's destructive plays directly, the possession of sente is actually in the balance for a while. You only find out who has it when the dust settles.

A mutual damage contest can be set off by miai: one player doesn't accept the idea that the other will get both of a pair of closely equivalent plays that are ordinarily sente. It can end in a game of 'chicken' (less colloquially, who blinks first).

Mutual damage in the opening is unusual.


An endgame which mutual damage is needed

[Diagram]

Question starts here

B1 is a typical endgame hane, which threatens heavy damage to White's territory if unanswered.

BillSpight: It is also what is normally called a double sente. It is worth around 9 points (miai), I believe, a huge play.


No mutual damage - loss

[Diagram]

No mutual damage

Locally, the sequence comes to an pause after W4 and Black has sente. He then uses his sente to execute another endgame hane.



Experienced players will agree the game is finished after White W8, and it is easy to see that Black wins by 3 points. It feels not entirely fair that Black has been able to play both hanes. Indeed, White has failed to apply the principle of mutual damage.


Mutual damage - may win

[Diagram]

Mutual damage

Mutual damage is in fact an application of the miai concept to the endgame. The moment Black plays B1 to damage White's territory, White must play the equivalent play at W2, if only out of self respect.



BillSpight: W2 and answering B1 are worth about the same. However, as Dieter says, White cannot afford to let Black get both hanes. It looks like White should play White a - Black b before W2. If Black has to play both points later, White a is aji keshi, but both sides will be invading, and this may be White's chance to inject some aji into Black's position. A difficult question.

See also Costly atari.

If B defends - loss

[Diagram]

B defends - loss by 1 point

If Black answers White's hane, White keeps sente to defend against Black's hane at W6. The game ends after W8; and White wins by 1 point.


If B damages W too

[Diagram]

Mutual damage

One reason many players fail to apply mutual damage, is that the situation can become very confused if either player refuses to give in as in this diagram.



Another reason is that the situation rarely is as symmetric as in this simple example. Even here it isn't quite symmetric: White a is atari whereas Black b is not.

BillSpight: And White c threatens a snapback at d.

aLegendWai: A difficult question. But who will win finally?


aLegendWai: It is my little opinion. You may disagree. Mutual damage should be used somewhat like a last-ditch approach, say, in a situation if you will lose when you complete the endgame peacefully.

Hmm that doesn't sound too sensible to me, Mutual Damage is an important principle in Go, especially in yose. If you don't apply it you never get sente and lose a lot of points.

aLegendWai: Wait a moment! Maybe we refer to different situations. Anyway, try to make it clear first. I focus mainly on the issue in the endgame, and in a situation where playing elsewhere will suffer a lot. (Just like the one in the above example). I don't even consider this play unless I know I am losing (so mutual damage is the only option). The reason why I won't play it because it is complex (a lot of uncertainities during both invasions). I can't be sure if I can gain if both invasion appears to make similar damages visually. That's why I feel it is somewhat a last-ditch approach. What do you think?

[Diagram]

Mutual damage - W is no hope

aLegendWai: But mutual damage may not lead to winning. It is true only if you can damage more than your opponent does!

Rich|ALegendWai, please read the first sentence on the page: "...provided one can inflict equivalent damage on the opponent."

aLegendWai: Thanks for telling. But I've noticed the existence of the statement already. I repeat here as an introduction for the diagram and that case.

aLegendWai: In the above example, I think mutual damage is no hope to W unfortunately.

I would like to know if there's an easy way to judge if a mutual damage is beneficial. Now it seems the only way to find out the answer is "try it out (in mind)"!

Rich: The answer is really 'read it out'. There just isn't an easy way to do everything, I'm afraid, or we'd all be playing perfectly.

aLegendWai: Hopefully someone will invent an easy way to evaluate the value of mutual damage. It will thus save a lot of brain cells :P (joking)


Still, if one player passively answers all "sente" endgame moves by the other, he or she follows a sure path to defeat.


TakeNGive (10k): Wow -- somehow I had never noticed this. Suddenly, BillSpight's endgame analyses take on new value.


Links:


Authors:


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This is a copy of the living page "Mutual Damage" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.
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